Sample interval modulation for the simultaneous acquisition of displacement vector data in magnetic resonance elastography: theory and application

Klatt, Dieter; Yasar, Temel Kaya; Royston, Thomas J.; Magin, Richard L.

doi:10.1088/0031-9155/58/24/8663

Cited by 46 publications

(62 citation statements)

References 33 publications

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“…The emergence of fractional encoding (encoding frequency higher than mechanical excitation frequency) has made possible to reduce the echo time and has led to new acceleration techniques such as multifrequency sequences . More recently, multidirectional sequences have been designed to reduce the number of acquisitions.…”

Section: Introductionmentioning

confidence: 99%

Interventional MR elastography for MRI‐guided percutaneous procedures

Corbin

Vappou

Breton

et al. 2015

Magnetic Resonance in Med

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Section: Introductionmentioning

confidence: 99%

Interventional MR elastography for MRI‐guided percutaneous procedures

Corbin

Vappou

Breton

et al. 2015

Magnetic Resonance in Med

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“…Scan parameters for all specimens are listed in Table . Magnetic resonance elastography was performed using a modified spin‐echo pulse sequence based on sample interval modulation MRE for the simultaneous acquisition of wave field displacement along all 3 Cartesian directions, as described in Refs and . The average MRE scan time was 34 minutes.…”

Section: Methodsmentioning

confidence: 99%

Prostate cancer assessment using MR elastography of fresh prostatectomy specimens at 9.4 T

Reiter

Majumdar

Kearney

et al. 2019

Magnetic Resonance in Med

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Purpose Despite its success in the assessment of prostate cancer (PCa), in vivo multiparametric MRI has limitations such as interobserver variability and low specificity. Several MRI methods, among them MR elastography, are currently being discussed as candidates for supplementing conventional multiparametric MRI. This study aims to investigate the detection of PCa in fresh ex vivo human prostatectomy specimens using MR elastography. Methods Fourteen fresh prostate specimens from men with clinically significant PCa without formalin fixation or prior radiation therapy were examined by MR elastography at 500 Hz immediately after radical prostatectomy in a 9.4T preclinical scanner. Specimens were divided into 12 segments for both calculation of storage modulus (G′ in kilopascals) and pathology (Gleason score) as reference standard. Sensitivity, specificity, and area under the receiver operating characteristic curve were calculated to assess PCa detection. Results The mean G′ and SD were as follows: all segments, 8.74 ± 5.26 kPa; healthy segments, 5.44 ± 4.40 kPa; and cancerous segments, 10.84 ± 4.65 kPa. The difference between healthy and cancerous segments was significant with P ≤ .001. Diagnostic performance assessed with the Youden index was as follows: sensitivity, 69%; specificity, 79%; area under the curve, 0.81; and cutoff, 10.67 kPa. Conclusion Our results suggest that prostate MR elastography has the potential to improve diagnostic performance of multiparametric MRI, especially regarding its 2 major limitations: interobserver variability and low specificity. Particularly the high value for specificity in PCa detection is a stimulating result and encourages further investigation of this method.

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“…Magnetic resonance elastography (MRE) allows the in vivo determination of local tissue shear stiffness using time‐resolved measurements of shear wave‐induced signal phase shifts . Recent technological advances in the field have focused on the development of actuator systems, wave inversion algorithms, improved image acquisition and motion encoding techniques …”

Section: Introductionmentioning

confidence: 99%

“…In addition to conventional sampling using equidistant phase offsets and sequential sampling of encoding directions and phases, encoding concepts utilizing temporally shifted MEGs with the simultaneous acquisition of multiple encoding directions, e.g. sample interval modulation (SLIM) and multidirectional reduced motion encoding (MD‐RME), have been proposed recently . SLIM encodes each motion component by varying the sampling interval to project each encoding direction to a different frequency, allowing the acquisition of the full motion field with only eight instead of 24 measurements.…”

Section: Introductionmentioning

confidence: 99%

“…SLIM encodes each motion component by varying the sampling interval to project each encoding direction to a different frequency, allowing the acquisition of the full motion field with only eight instead of 24 measurements. However, the original suggestion of only temporally shifting the MEGs necessitates prolonged TEs to freely shift the MEGs within 1.875 wave periods . MD‐RME utilizes a similar concept to SLIM, but was designed using a framework for optimization‐based sequence design for MRE.…”

Section: Introductionmentioning

confidence: 99%

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Analysis and improvement of motion encoding in magnetic resonance elastography

et al. 2018

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Magnetic resonance elastography (MRE) utilizes phase contrast magnetic resonance imaging (MRI), which is phase locked to externally generated mechanical vibrations, to measure the three-dimensional wave displacement field. At least four measurements with linear-independent encoding directions are necessary to correct for spurious phase contributions if effects from imaging gradients are non-negligible. In MRE, three encoding schemes have been used: unbalanced four- and six-point and balanced four-point ('tetrahedral') encoding. The first two sensitize to motion with orthogonal gradients, with the four-point method acquiring a single reference scan without motion sensitization, whereas three additional scans with inverted gradients are used with six-point encoding, leading to two-fold higher displacement-to-noise ratio (DNR) and 50% longer scan duration. Balanced four-point (tetrahedral) encoding encodes along the four diagonals of a cube, with one direction serving as a reference for the other three encoding directions, similar to four-point encoding. The objective of this work is to introduce a theoretical framework to compare different motion sensitization strategies with respect to their motion encoding efficiency in two fundamental encoding limits, the gradient strength limit and the dynamic range limit, which are both placed in relation to conventional gradient recalled echo (GRE)- and spin echo (SE)-based MRE sequences. We apply the framework to the three aforementioned schemes and show that the motion encoding efficiency of unbalanced four- and six-point encoding schemes in the gradient-limited regime can be increased by a factor of 1.5 when using all physical gradient channels concurrently. Furthermore, it is demonstrated that reversing the direction of the reference in balanced four-point (tetrahedral) encoding results in the Hadamard encoding scheme, which leads to increased DNR by 2 compared with balanced four-point encoding and 2.8 compared with unbalanced four-point encoding. As an example, we show that optimal encoding can be utilized to reduce the acquisition time of standard liver MRE in vivo from four to two breath holds.

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Sample interval modulation for the simultaneous acquisition of displacement vector data in magnetic resonance elastography: theory and application

Cited by 46 publications

References 33 publications

Interventional MR elastography for MRI‐guided percutaneous procedures

Interventional MR elastography for MRI‐guided percutaneous procedures

Prostate cancer assessment using MR elastography of fresh prostatectomy specimens at 9.4 T

Analysis and improvement of motion encoding in magnetic resonance elastography

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